Conventional hybrid vehicles, which are improved in fuel saving by driving with a motor in addition to an engine, compensate for motor drive or other necessary electrical power by power of a battery embedded in the vehicle. These hybrid vehicles control charge and discharge by charging the battery with kinetic energy used as regenerative electric power during deceleration.
In this type of hybrid vehicle, it is difficult to maintain the running and the vehicle system if discharge continues when the battery residual quantity is extremely low. This type of hybrid vehicle may also lead to degradation and malfunction of battery performance when excessive amounts of charges and discharges of the battery continue for a long period of time.
Therefore, in the hybrid vehicle, a control method for limiting incoming and outgoing electric current is needed in light of battery protection. A control method of a high-order controller of controlling a system to limit the incoming and outgoing electric current is known as such a control method (See Patent Document 1, for example).